1. Field of the Invention
The present invention relates to a fuel-flow-rate control device for controlling a fuel flow rate of a gas turbine, to a power generation system, and to a method for controlling a fuel flow rate.
This application is based on Japanese Patent Application No. 2005-260579, the content of which is incorporated herein by reference.
2. Description of Related Art
Heretofore, the method disclosed in Japanese Unexamined Patent Application Publication No. 6-193471 (FIG. 2) is a known fuel-flow-rate control method for gas turbines installed in gas turbine power generation facilities and the like.
According to Japanese Unexamined Patent Application Publication No. 6-193471, first, second, and third fuel flow rates are calculated. The first fuel flow rate is for maintaining a desired revolution speed of a gas turbine, the second fuel flow rate is for maintaining a desired temperature of an exhaust gas emitted from the gas turbine, and the third fuel flow rate is for controlling the acceleration so that an inlet temperature of the turbine does not reach a predetermined maximum temperature. In addition, the third fuel flow rate is corrected based on an outlet air temperature of a heat exchanger. A technique in which a fuel flow rate supplied to a combustor is controlled to the smallest fuel flow rate among the first fuel flow rate, the second fuel flow rate, and the corrected third fuel flow rate is also disclosed.
However, in a gas turbine of the related art, when the load is increased in a low-load region including a starting time and when the load is increased in a high-load region in response to a reset operation of a down command for automatic frequency control, there is a problem of overshooting of the inlet temperature of the gas turbine due to the following reasons.
Specifically, in the system of the related art, control is first performed using the revolution speed of the turbine or the fuel flow rate based on a power generator output command, and subsequently, when the gas turbine output is increased to the vicinity of a base load (rated output point), the control method is changed to a method based on temperature, such as the exhaust gas temperature, and the gas turbine output is stabilized at the rated output point. However, during the temperature control, because of a response delay, the gas turbine output may temporarily overshoot the rated output point in some cases, and in association with this overshooting, the gas turbine inlet temperature also overshoots.
Heretofore, in order to suppress this overshooting of the gas turbine inlet temperature, for example, the following methods have been used: a fuel-flow-rate control method in which the rate of change in the load is decreased, and a fuel-flow-rate control method in which the control based on the turbine revolution speed is changed to the control based on the temperature at an early stage. However, neither of the control methods described above are suitable for reducing the starting time, and hence a control method which can shorten the starting time and which can simultaneously improve the efficiency of power generation has been desired.